1910.] Vegetable Assimilation and Respiration. 447 



rate as during the latter part of the experiment, another 3 or 4 milHgrammes 

 must be added, making the total rate 17 or IS milligrammes. 



In the light, however, of the high rate of increase shown by detached leaves 

 of Hdianthiis annuus this value for the sugar beet is by no means incredible, 

 Especially when we consider that the air near the ground is more highly 

 charged with carbon dioxide than is the normal atmosphere ; no doubt is 

 therefore thrown upon the assumption of translocation which was made in 

 obtaining this value. 



Other evidence. — The same assumption also makes possible the interpretation 

 of some of Miiller's results.* Several of his comparative experiments with 

 Monocotyledons and Dicotyledons appear to indicate that leaves of the former 

 class increase in weight much more rapidly to begin with than leaves of 

 Dicotyledons, continue assimilating at their full capacity for a shorter time, 

 and translocate the products much more slowly. 



It appears possible that both the greater rapidity and the shorter duration 

 of the initial increase in Monocotyledons are to be explained by reference to 

 the slow translocation. If it be assumed that translocation continues side by 

 side with assimilation, the more rapid translocation in Dicotyledons would 

 reduce the net increase in weight more than the slow translocation in 

 Monocotyledons ; and in the latter, ceteris ])aribus, repletion would be reached 

 more quickly.t 



This slower translocation in Monocotyledons is probably connected with 

 characteristic structural and biological features, such as the relatively small 

 and slowly growing stem, and the long parallel-veined leaves. It would indeed 

 be strange were the rate of translocation found to be independent of such 

 features. The whole subject of translocation is one which promises a rich 

 and varied field for research, and calls for the united efforts of physiologist 

 and physiological anatomist in its investigation. 



Section V. — Summary. 

 1. In this paper it is proved that in the open air high rates of assimilation 

 occur notwithstanding the small concentration of COg present in the 

 atmosphere. 



2a. In the experiments with Heliantlius annuus, which agree very closely 

 among themselves, leaves v:hich remained tm^gid, and so Icept their stomata 

 * Loc. cit. 



t By these experiments and others in which he forced assimilation with excess of COj 

 for several days, Miiller also concluded that Monocotyledons (or rather sugar-leaves) 

 reach their maximum content of photosynthetic products more quickly, but that this 

 maximum is much lower than in Dicotyledons (starch-leaves). 



